1. Field of the Invention
The present invention relates to processing for localizing sound images, more particularly to virtual localization processing to a plurality of listeners.
2. Description of the Prior Art
Reproduction of multi-channel-audio-signals is performed with a front center speaker, a surround left speaker, and a surround right speaker in addition to speakers arranged at the front left and the front right side to the listener. Both the surround left speaker and the surround right speaker are arranged at either beside the listener or backward thereto, and sound field just as enveloping the listener is reproduced therewith. Devices, which reproduce the sound field as a virtual sound source, have been proposed due to the limitation in spaces for speaker placement. In such device, signals for front left channel, front center channel, and front right channel are respectively provided to the front left speaker, the front center speaker, and the front right speaker. As depicted in FIG. 31, both a surround left channel signal SL and a surround right channel signal SR are processed with filters 6a, 6b, 6c, 6d and the resulting signals are provided to both a front left speaker 4L and a front right speaker 4R. The listener feels like that speakers XL and XR are arranged at positions behind him/her if transfer functions H11, H12, H21, and H22 of the filters 6a, 6b, 6c and 6d are respectively represented by the following equations:
Here, hRL is a transfer function from the speaker 4R to the left ear 2L of the listener 2, hRR is a transfer function from the speaker 4R to the right ear 2R of the listener 2; hLL is a transfer function from the speaker 4L to the left ear 2L of the listener 2, hLR is a transfer function from the speaker 4L to the right ear 2R of the listener 2.
In this way, a sound source reproducing the sound field through which the listener feels that he/she is surrounded therewith, is obtained without placing surround speakers beside and/or behind the listener.
Another method having much simple processes, in which the reproduction of both the surround left channel signal SL and the surround right channel signal SR is carried out by a phase shift control without performing virtual localization processing, has been proposed as depicted in FIG. 32, the surround left channel signal SL and the surround right channel signal SR being processed under the phase difference control such that just reversing their phases.
In the device depicted in FIG. 31, however, the positions of the listener 2 where enable to obtain the surround sound source are strictly limited to a certain area located along with a central axis 8 extending between the listener 2 and the middle point between the front left and the front right speakers. Consequently, it is substantially impossible for the device to provide an appropriate surround-effect simultaneously to listeners if two or more of them exist.
In the method as depicted in FIG. 32, there is a high probability that the sound field reproduced with the surround signals is undesiredly localized at positions out of the certain area because symmetry between the speakers 4R and 4L relative to the central axis 8 is not satisfied at positions away from the central axis 8.
The primary object of the present invention is to overcome the above mentioned problems and to provide a surround signal processing system capable of obtaining the surround sound source localized virtually even when a plurality of listeners sit next to each other under side-by-side basis. Another object of the present invention is to provide a surround signal processing system with simple structure capable of localizing sound field without causing undesired shift in localization even when a plurality of listeners sit next to each other under side-by-side basis.